This invention relates to fuel cells and, in particular, to a reforming catalyst for use with such fuel cells.
A fuel cell is a device which directly converts chemical energy stored in hydrocarbon fuel into electrical energy by means of an electrochemical reaction. Generally, a fuel cell comprises an anode and a cathode separated by an electrolyte, which serves to conduct electrically charged ions. In order to produce a useful power level, a number of individual fuel cells are stacked in series with an electrically conductive separator plate between each cell.
In internally reforming fuel cells, a reforming catalyst is placed within the fuel cell stack to allow direct use of hydrocarbon fuels such as methane, coal gas, etc. without the need for expensive and complex reforming equipment. In a reforming reaction, fuel cell produced water and heat are used by the reforming reaction, and the fuel is internally reformed to produce hydrogen for fuel cell use. Thus, the endothermic reforming reaction can be used advantageously to help cool the fuel cell stack.
Two different types of direct fuel cell assemblies have been developed. One type of reforming is indirect internal reforming, which is accomplished by placing the reforming catalyst in an isolated chamber within the stack and routing the reformed gas from this chamber into the anode compartment of the fuel cell. A second type of reforming is direct internal reforming. This type of reforming is accomplished by placing the reforming catalyst within the active anode compartment, which provides the hydrogen produced by the reforming reaction directly to the anode. In particular, the reforming catalyst for direct internal reforming is typically placed in corrugations of an anode current collector of the anode compartment. The reforming catalyst is usually available in various compacted solid shapes such as tablet, pellet, rod, ring or sphere form. Typical techniques for incorporating these types of catalysts in the corrugated anode current collector are described in U.S. Pat. No. 4,788,110. These techniques, however, are difficult to automate and are therefore not cost effective due to the small size of the catalyst particles. Moreover, the catalyst placed in the anode current collector using these techniques often shifts or spills during assembly, handling, transportation and operation.
To overcome these disadvantages, U.S. Patent Application Publication No. 2004/0157104, assigned to the same assignee herein, discloses a reforming catalyst formed as a continuous cord by extrusion and a method of loading this catalyst into the current collector which is automatically carried out in-situ using a PC controller, an extruder with a nozzle or head and an X-Y position table. However, while the catalyst cords formed using the method of the 2004/0157104 publication have an active surface area which provides a desired utilization of the catalyst, it would be beneficial to increase the active surface area to provide enhanced utilization. Moreover, the extrudate catalyst prepared using this method often may loosely adhere to the anode corrugations in which it is deposited. This can lead to curling and falling off of the catalyst from the corrugations. Providing a stronger bond between the catalyst and corrugations would therefore also be desirable.
It is therefore an object of the present invention to provide an improved reforming catalyst extrudate with enhanced diffusion and catalytic activity.
It is also an object of the present invention to provide a catalyst extrudate which results in materials costs reduction.
It is a further object of the present invention to provide a method of loading the catalyst extrudate which improves adhesion characteristics between the catalyst and the anode current collector corrugations.